Soil-Structure Interaction Seminar - Foundation Performance ...

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Landscaping in North and West Houston, where sandy, non-expansive soils are present, with flowers and shrubs should not pose a major problem next to the foundations . This condition assumes that the foundations are designed for saturated soil conditions. Major foundation problems can occur if the planter areas are saturated as the foundations are not designed for saturated (perched water table) conditions. The problems can occur in a form of foundation settlement, brick cracking, etc. Sprinkler systems can be used in the areas where expansive soils are present, provided the sprinkler system is placed all around the house to provide a uniform moisture condition • throughout the year. The use of a sprinkler system in North and West Houston where sandy soils are present should not pose any problems, provided the foundations are designed for saturated subsoil conditions with positive drainage away from the structure. The excavations for the sprinkler system lines, in the areas where expansive soils are present, should be backfilled with impermeable clays. Bank sands or top soil should not be used as backfill. -Ttrese soils should be properly compacted to minimize water flow into the excavation trench and seeping under the foundations, resulting in foundation and structural distress. The sprinkler system must be checked for leakage at least once a month. Significant foundation movements can occur if the expansive soils under the foundations are exposed to a source of free water. The homeowner should also be aware of damage that leaking plumbing or underground utilities can cause, if they are allowed to continue leaking and providing the expansive soils with the source of water. The presence of trees near a residence is considered to be a potential contributing factor to the foundation distress. Our experience shows that large trees in close proximity to residential structures can cause foundation and soil settlements. This problem is aggravated by cyclic wet and dry seasons in the area. Foundation damage of residential structures caused by the adjacent trees indicates that foundation movements of as much as 3- to 4-inches can be experienced in close proximity to residential foundations. This condition will be more severe in the periods of extreme drought. Sometimes the root system of trees such as willow or oak can physically move foundations and walls and cause considerable structural damage. Root barriers can be installed near the exterior grade beams to a minimum depth of 36-inches, if trees are left in place in close proximity to foundations. It is recommended that trees not be planted closer than half the canopy diameter of the mature tree, typicaJly 20-feet from foundations. Any trees in closer proximity should be thoroughly soaked at least twice a week during hot summer months, and once a week in periods of low rainfall. GEOTECH ENGINEERING AND TESTING, INC. -------------· 21
Inspections Every homeowner should conduct a yearly observation of foundations and flatworks and perform any maintenance necessary to improve drainage and minimize infiltrations of water from rain and lawn watering. This is important especially during the first six years of a newly built home because this is usually the time of the most severe adjustment between the new construction and its environment. Some cracking may occur in the foundations. For example, most concrete slabs can develop • hairline cracks. This does not mean that the foundation has failed. All cracks should be cleaned up of debris as soon as possible. The cracks should be backfilled with high-strength epoxy glue or similar materials. If a foundation experiences significant separations, movements, cracking, the owner must contact the builder and the engineer to find out the reason(s) for the foundation distress and develop remedial measures to minimize foundation problems:-· General I FOUNDATION STABILIZATION Several methods of foundation stabilization are presented here. These recommendations include foundation underpinning, using drilled footings or jacked precast piles, moisture barriers, moisture stabilization, and chemical stabilization. Some of these methods are being used in the Houston area. A description of each method is summarized in the following sections of this document. Foundation Underpinning Foundation Underpinning, using drilled footings or precast driven piles has been used in the Houston area for a number of years. The construction of a drilled footing consists of drilling a shaft, about 12-inches in diameter (or larger) underneath a grade beam. The shaft is generally extended to depths ranging from 8 to 12-feet below existing grade. The bottom of the shaft is then reamed with an underreaming tool. The hole is then backfilled with steel, concrete, and the grade beams are jacked to a level position and shimmied to level the foundation system. In a case of jacked precast piers, precast concrete piers are driven into the soils. These pier attain there bearing capacity based on the end bearing and the skin friction. In general, the precast concrete piers are about 12-inches in height, six-inches in diameter and jacked into the soil. It is important the precast pier foundations are driven below the active zone to resist the uplift loads as a result of underlying expansive soils. Some of these jacked piles may consist of perma-piles, ultra piles, cable lock piles, etc. GEOTECH ENGINEERING AND TESTING, INC. -------------· 22
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SOIL STRUCTURE INTERACTION SEMINA
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FOUNDATION FAILURE DEFINED IN TERMS
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FOUNDATION FAILURE DEFINED IN TERMS
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FOUNDATION FAILURE IN THE HOUSTON A
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FOUNDATION FAILURES IN THE HOUSTON
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Inspections of the foundation had b
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J CASE NO. 10 - THE USE OF SPREAD F
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GARAGE 0" ·-0.2" -0.8 11 -0.3" •
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V) IJ.J u
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• +0.3" +0.5" • 0 10 I SCALE IN
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CURRENT PRACTICES FOR DESIGN OF TRA
Page 42 and 43: INTRODUCTION CURRENT PRACTICES FOR
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Page 62: I I. I I APPENDIX B TYPICAL GENERAL
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Page 72 and 73: GUIDLINES FOR GEOTECHNICAL DESIGN,
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Page 76 and 77: INTRODUCTION The variable subsoil c
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Page 83 and 84: Foundation Design Considerations In
Page 85 and 86: Vegetation Control We recommend tre
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Page 89 and 90: Concrete Placement Monitoring The c
Page 91: Area drains can be used around the
Page 95 and 96: Moisture Barriers Moisture barriers
Page 97: RECOMMENDED QUALITY CONTROL AND INS
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Page 110 and 111: PROFESSIONAL RESUME of DONALD E. LE
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Page 119: A P P E N D I X- DRAWINGS SAMPLE FO
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Section 6-52. Exceptions CITY OF WE
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Soil Structure Interaction Seminar
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July 21, 1994 Page3 corporation, as
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Residential Construction Liability
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July 21, 1994 Page 8 E. Defenses to
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The Texas Deceptive Trade Practices
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construction or design of the house
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(5) Arguably, implied warranties do
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(3) Includes any diminution in mark
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D. Who Is a Proper Plaintiff? 1. An
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a. claimant's damages are limited t
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a. May be based on hearsay (i.e., e
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d. The Broker (1) Absent specific a
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VI. More Honored in the Breach HORA
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